CAMBRIDGE INTERNATIONAL EXAMINATIONS
Cambridge International General Certificate of Secondary Education
MARK SCHEME for the October/November 2014 series
0620 CHEMISTRY
0620/31
Paper 3 (Extended Theory), maximum raw mark 80
Mark schemes should be read in conjunction with the question paper and the Principal Examiner
Report for Teachers.
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This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of
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Page 2
1
Mark Scheme
Cambridge IGCSE – October/November 2014
Syllabus
0620
Paper
31
(a) Match the following pH values to the solutions given below.
1
3
7
10
13
The solutions all have the same concentration.
solution
aqueous ammonia, weak base
dilute hydrochloric acid, a strong acid
aqueous sodium hydroxide, a strong base
aqueous sodium chloride, a salt
dilute ethanoic acid, a weak acid
pH
10
1
13
7
3
[5]
(b) Hydrochloric acid strong acid or ethanoic acid weak acid
OR: hydrochloric acid completely ionised or ethanoic acid
partially ionised
hydrochloric acid greater concentration of/more H+ ions (than ethanoic acid)
[1]
(c) Rate of reaction with Ca, Mg, Zn, Fe
[1]
[1]
Strong (hydrochloric) acid bubbles faster or more bubbles or dissolves faster
[1]
OR: rate of reaction with (metal) carbonate
strong (hydrochloric) acid faster or more bubbles or dissolves faster (only if
carbonate insoluble)
[1]
[1]
OR: electrical conductivity
strong (hydrochloric) acid better conductor
[1]
[1]
[Total: 9]
2
(a) soft because weak forces between layers/sheets/rows
[1]
layers can slip/slide
[1]
good conductor because electrons can move/mobile
[1]
(b) it is soft: pencils or lubricant or polish
good conductor: electrodes or brushes (in electric motors)
[1]
[1]
(c) (i) every silicon atom is bonded/attached to 4 oxygen atoms or every oxygen
bonded/attached to two silicon atoms
[1]
(ii) Any two from:
high melting point/boiling point
hard
colourless crystals/shiny
poor/non-conductor of electricity/insulator
insoluble in water
[2]
[Total: 8]
© Cambridge International Examinations 2014
Page 3
3
Mark Scheme
Cambridge IGCSE – October/November 2014
Syllabus
0620
Paper
31
(a) Any two from:
bleach/making wood pulp/making paper
food/fruit juice/wine preservative
fumigant/sterilising/insecticide
[2]
(b) heating/roasting/burning (zinc sulfides)
in air/oxygen COND on M1
[1]
[1]
(c) (i) V2O5
[1]
(ii) position of equilibrium shifts right/yield increases
to save energy
[1]
[1]
(iii) faster reaction/rate
[1]
more collisions per second/higher collision frequency
[1]
fewer moles/molecules (of gas) on right
[1]
(so) position of equilibrium shifts right/yield increases
[1]
(d) (the reaction is) too violent/too exothermic or produces mist/fumes (of acid)
[1]
[Total: 12]
4
(a) (i) insufficient/limited oxygen
or 2C + O2 → 2CO
coke/carbon reacts with carbon dioxide
or C + CO2 → 2CO
(ii) Fe2O3 + 3CO → 2Fe + 3CO2
species (1) balancing (1)
(b) (i) carbon dioxide
[1]
[1]
[2]
[1]
(ii) CaO + SiO2 → CaSiO3
[1] each side correct
[2]
(iii) (molten) iron higher density (than slag)
[2]
(iv) No oxygen in contact with iron or layer of slag prevents hot iron reacting with
oxygen/air or (all) oxygen reacts with carbon (so no oxygen left to react with
iron)
(c) (i) air/oxygen and water (need both)
© Cambridge International Examinations 2014
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Page 4
Mark Scheme
Cambridge IGCSE – October/November 2014
Syllabus
0620
(ii) aluminium oxide layer is impervious or non-porous or passive or unreactive
or will not allow water/air to pass through it (rust allows passage of water or
air or it flakes off)
(d) (i) zinc more reactive (than iron/steel)
loses electrons
electrons move (from zinc) to iron
Zinc reacts (with air and water) or zinc corrodes or zinc is oxidised or zinc is
anodic or zinc forms positive ions or zinc forms Zn2+ or iron and steel don’t
react with air/water or iron and steel are not oxidised or iron and steel do not
form ions or iron and steel do not lose electrons or iron and steel are
cathodic
(ii) R to L in wire
Paper
31
[1]
[1]
[1]
[1]
[1]
[1]
(iii) 2H+ + 2e– → H2
species (1) balancing (1)
[Total: 19]
5
(a) nitrogen and oxygen react
at high temperatures (in engine)
[1]
[1]
(b) M1 carbon monoxide (converted to) carbon dioxide or 2CO + O2 → 2CO2
[1]
M2 (by) oxides of nitrogen (which are reduced to) nitrogen
or 2NO → N2 + O2 or 2NO2 → N2 + 2O2
[1]
M3 hydrocarbons (burn) making water
[1]
M4 products: any two from:
carbon dioxide, water, nitrogen
[1]
(c) lead compounds are toxic or brain damage or reduce IQ or nausea or kidney
failure or anaemia
[1]
[Total: 7]
6
(a) (i) butanoic acid
methanol
[1]
[1]
(ii) number of moles of ethanoic acid = 0.1
number of moles of ethanol = 0.12(0)
the limiting reagent is ethanoic acid
number of moles of ethyl ethanoate formed = 0.1
maximum yield of ethyl ethanoate is 8.8 g
© Cambridge International Examinations 2014
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[1]
[1]
[1]
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Page 5
Mark Scheme
Cambridge IGCSE – October/November 2014
Syllabus
0620
Paper
31
(b) correct ester linkage [1]
two ester linkages (COND on M1)
continuation (COND on M2)
[1]
[1]
(c) (i) add bromine water/bromine
turns colourless
remains brown/orange/reddish brown/yellow
[1]
[1]
[1]
ALLOW: potassium manganate(VII) (acidic or alkaline)
correct colour colourless/green or brown ppt
stays pink/purple
[1]
[1]
[1]
(ii) ester 1
COND alkyl group is CnH2n+1 which is NOT C17H33
or C17H35 is CnH2n+1 or less hydrogen
[1]
(iii) soap or (sodium) salt (of a carboxylic acid) or carboxylate
[1]
alcohol
[1]
[1]
[Total: 17]
7
(a) (i) 6Li + N2 = 2Li3N
species (1) balancing (1)
(ii) N3– ion drawn correctly
Charges correct (minimum 1 × Li ion and 1 nitride ion)
(b) (i) 3 × shared pairs between N and 3 × F
only 2 non-bonding electrons on N, 6 non-bonding electrons on each F
(COND on first point)
(ii) Strong attractive forces/strong ionic bonds in lithium nitride
weak (attractive) forces between molecules in NF3
[1]
[1]
[1]
[1]
[1]
[1]
[Total: 8]
© Cambridge International Examinations 2014